FIELD OF THE INVENTION
The present invention relates generally to the field of a rotation detector for detecting the number of revolutions or the speed of rotation, such as a rotation detecting apparatus that is specifically intended for use in detecting the number of revolutions or the speed of rotation for wheels on an automotive vehicle. More particularly, the present invention relates to a tone wheel that may be included in such rotation detecting apparatus together with a rotation sensor for detecting the number of revolutions, wherein the tone wheel is provided for enhancing the sensing ability of the rotation sensor, or the rotation detecting apparatus incorporating the rotation sensor, to detect the number of revolutions or the speed of rotation with higher precision.
Typically, the rotation detecting apparatus of the type described above is mounted on an automobile vehicle so that it can flexibly control the vehicle safety driving mechanism, such as the antilock braking system, the traction control system, the stability control system and the like, which is also installed on the automotive vehicle. Specifically, this rotation detecting apparatus is located on the hub flange and the like in the vehicle's suspension system, and is used for detecting the actual number of revolutions/the speed of rotation for the wheels. When there is any difference in the number of revolutions/the speed of rotation between each of the front wheels and/or between each of the rear wheels that may be determined from the actual number of revolutions/the speed of rotation thus detected, the vehicle driving system or the braking system may be turned on or off, thereby controlling the behavior of the vehicle. This is to ensure that the vehicle can be running with safety in case any emergency situation should occur.
Typically, the rotation detecting apparatus is constructed by incorporating the tone wheel and the rotation sensor therein, as described below in detail. Generally, the tone wheel includes a seal having a flange extending radially and a radial annular ring formed by the flange. The radial annular ring is made of any magnetizable material and magnetized. Within the rotation detecting apparatus, the rotation sensor is located in proximity to the magnetized annular ring of the tone wheel, so that it can detect the number of revolutions/the speed of rotation in response to a pulse from the magnetized annular ring that represents the actual number of revolutions/speed of rotation.